I don't think Chinese support for NK has ever been a secret anymore than the the US support for South Korea has. And it's in China's backyardd so they've got way more of an excuse.
And if you think that doesn't matter, look at the Monroe Doctrine [1].
Taken further, the so-called Cuban Missile Crisis should really be called the Turkey Missile Crisis. The US (through NATO) placed Jupiter nuclear MRBMs in Turkey, only hunddreds of miles from Moscow. The USSR responded by doing the exact same thing, by placing nuclear weapons in Cuba. And the US almost started World War 3 over it.
It was the USSR who stepped back from the brink and, as a result of a secret agreement, the Jupiter MRBMs were quietly removed from Turkey [2].
And if you think that doesn't matter, look at the Monroe Doctrine [1].
Taken further, the so-called Cuban Missile Crisis should really be called the Turkey Missile Crisis. The US (through NATO) placed Jupiter nuclear MRBMs in Turkey, only hunddreds of miles from Moscow. The USSR responded by doing the exact same thing, by placing nuclear weapons in Cuba. And the US almost started World War 3 over it.
It was the USSR who stepped back from the brink and, as a result of a secret agreement, the Jupiter MRBMs were quietly removed from Turkey [2].
[1]: https://en.wikipedia.org/wiki/Monroe_Doctrine
[2]: https://www.wilsoncenter.org/blog-post/jupiter-missiles-and-...